Support Double Values

[jamadden]

This was requested on the BTrees mailing list:

On Mar 14, 2019, at 13:16, Tres Seaver wrote:

On 3/14/19 10:28 AM, Qiwen Chen wrote:
Is there an easy to extend the F (32-bit C float) type in BTrees ( such as IFBTree, LFBTree) to a DOUBLE type?
I currently use IOBTree and LOBTree for storing double type. But I would assume it's not as efficient.

There is no knob to allow that. You could cobble it together yourself, following the pattern for the float-value trees:

• Copy 'BTrees/floatvalue.h' -> 'doublevalue.h' and make the appropriate changes (figure out which Python API calls need to change).
• Add new interfaces to 'BTrees/Interfaces.py' (IIntegerDoubleBTreeModule, ILongDoubleBTreeMoudle)
• Copy 'BTrees/_IFBTree.c' -> '_IDBTree.c' and make appopriate changes ('#include "doublevaluemacros.h"', etc. Ditto for 'BTrees/LFBTree.c'.
• Copy 'BTrees/IFBTree.py' -> 'IDBTree.py' and make appropriate changes. Ditto for 'BTrees/LFBTree.py'.
• Copy 'BTrees/tests/test_IFBTree.py' and make appropriate chagnes. Ditto for 'BTrees/tests/test_LFBtree.py'. You could maybe skip this part, but they would be required if you wanted to get your branch merged.
• Update 'setup.py' to add the new 'FLAVORS' and 'FAMILIES' values.
• Test thoroughly, including measuring RAM saved over the 'IO' / 'LO' variants. :)

[jamadden]

#123 makes this easier.